Porous metal oxide microspheres

ABSTRACT

Porous metal oxide microspheres are prepared via a process comprising forming a liquid dispersion of polymer nanoparticles and a metal oxide; forming liquid droplets of the dispersion; drying the droplets to provide polymer template microspheres comprising polymer nanospheres; and removing the polymer nanospheres from the template microspheres to provide the porous metal oxide microspheres. The porous microspheres exhibit saturated colors and are suitable as colorants for a variety of end-uses.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 16/126,338, filed on Sep. 10, 2018, which claims the benefit ofpriority of U.S. Provisional Patent Application No. 62/556,792, filed onSep. 11, 2017, the disclosures of which are hereby incorporated byreference herein in their entireties.

BACKGROUND

Traditional pigments and dyes exhibit color via light absorption andreflection, relying on chemical structure. Structural colorants exhibitcolor via light interference effects, relying on physical structure asopposed to chemical structure. Structural colorants are found in nature,for instance in bird feathers, butterfly wings and certain gemstones.Structural colorants are materials containing microscopically structuredsurfaces small enough to interfere with visible light and produce color.Such materials may be based on photonic materials including, but notlimited to, opals, inverse opals, photonic granules, photonic spheres orcomposite photonic crystals. The term “photonic material” refers to amaterial having a degree of periodic variations in its structure.

Structural colorants may exhibit high stability. Accordingly, desiredare structural colorants that exhibit different colors of visible lightobservable to the naked eye when present in bulk. Such structuralcolorants may be formulated into consumer products as a replacement forless stable and/or less environmentally friendly pigments or dyes.

It has been found that certain porous metal oxide microspheres exhibithigh quality color in bulk. The microspheres provide color visible inthe bulk.

SUMMARY

Accordingly, disclosed is a method to prepare porous metal oxidemicrospheres comprising a metal oxide, the method comprising forming aliquid dispersion of polymer nanoparticles and a metal oxide; formingliquid droplets of the dispersion; drying the liquid droplets to providepolymer template microspheres comprising polymer nanospheres and metaloxide; and removing the polymer nanospheres from the templatemicrospheres to provide the porous metal oxide microspheres.

Also disclosed are porous microspheres comprising a metal oxide, whereinthe microspheres have an average diameter of from about 0.5 μm to about100 μm, an average porosity of from about 0.10 to about 0.90 or fromabout 0.10 to about 0.80 and an average pore diameter of from about 50nm to about 999 nm.

Also disclosed are porous microspheres comprising a metal oxide, whereina bulk sample of the porous microspheres exhibits color observable bythe human eye.

Disclosed also are compositions comprising a substrate and the presentporous microspheres; for example where the compositions are aqueousformulations, oil-based formulations, coatings formulations, foods,inks, plastics, cosmetic formulations or materials for medicalapplications or security applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure described herein is illustrated by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, features illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some featuresmay be exaggerated relative to other features for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements.

FIG. 1 shows a general outline for the preparation of porousmicrospheres according to an embodiment of the invention.

FIG. 2 is a scanning electron microscope (SEM) image of a polymertemplate microsphere, according to an embodiment of the invention.

FIG. 3 is a SEM image of a porous silica microsphere, according to anembodiment of the invention.

FIG. 4 is a representation of a spray-drying process according to someembodiments of the invention.

DETAILED DESCRIPTION

Present metal oxide microspheres, or photonic balls, may be preparedwith the use of a polymeric sacrificial template. In one embodiment, anaqueous colloid dispersion containing polymer particles and a metaloxide is prepared, the polymer particles typically being nano-scaled.The aqueous colloidal dispersion is mixed with a continuous oil phase,for instance within a microfluidic device, to produce a water-in-oilemulsion. Emulsion aqueous droplets are prepared, collected and dried toform microspheres containing polymer nanoparticles and metal oxide. Thepolymer nanoparticles (nanospheres) are then removed, for instance viacalcination, to provide spherical, micron-scaled metal oxide particles(microspheres) containing a high degree of porosity and nano-scaledpores. The microspheres may contain uniform pore diameters, a result ofthe polymer particles being spherical and monodisperse.

FIG. 1 shows a general outline for the preparation of present porousmicrospheres. An emulsion droplet containing polymer nanospheres andmetal oxide is dried to remove solvent, providing an assembledmicrosphere containing polymer nanospheres with metal oxide in theinterstitial spaces between the polymer nanospheres (templatemicrosphere or “direct structure”). The polymer nanospheres define theinterstitial space. Calcination results in removal of the polymer,providing a present metal oxide microsphere with high porosity, or voidvolume (inverse structure).

The porous metal oxide microspheres are advantageously sintered,resulting in a continuous solid structure which is thermally andmechanically stable.

In some embodiments, droplet formation and collection occurs within amicrofluidic device. Microfluidic devices are for instance narrowchannel devices having a micron-scaled droplet junction adapted toproduce uniform size droplets connected to a collection reservoir.Microfluidic devices for example contain a droplet junction having achannel width of from about 10 μm to about 100 μm. The devices are forinstance made of polydimethylsiloxane (PDMS) and may be prepared forexample via soft lithography. An emulsion may be prepared within thedevice via pumping an aqueous dispersed phase and oil continuous phaseat specified rates to the device where mixing occurs to provide emulsiondroplets. Alternatively, an oil-in-water emulsion may be employed.

In some embodiments, vibrating nozzle techniques may be employed. Inthese techniques, a liquid dispersion is prepared, droplets are formedand are dropped into a bath of a continuous phase. The droplets are thendried followed by removal of the polymer. Vibrating nozzle equipment isavailable from Büchi and comprises for instance a syringe pump and apulsation unit. Vibrating nozzle equipment may also comprise a pressureregulation valve.

The polymer nanoparticles for instance have an average diameter of fromabout 50 nm to about 999 nm and are monodisperse.

Suitable template polymers include thermoplastic polymers. For example,template polymers are selected from the group consisting ofpoly(meth)acrylic acid, poly(meth)acrylates, polystyrenes,polyacrylamides, polyvinyl alcohol, polyvinyl acetate, polyesters,polyurethanes, polyethylene, polypropylene, polylactic acid,polyacrylonitrile, polyvinyl ethers, derivatives thereof, salts thereof,copolymers thereof and combinations thereof. For example, the polymer isselected from the group consisting of polymethyl methacrylate, polyethylmethacrylate, poly(n-butyl methacrylate), polystyrene,poly(chloro-styrene), poly(alpha-methyl styrene),poly(N-methylolacrylamide), styrene/methyl methacrylate copolymer,polyalkylated acrylate, polyhydroxyl acrylate, polyamino acrylate,polycyanoacrylate, polyfluorinated acrylate, poly(N-methylolacrylamide),polyacrylic acid, polymethacrylic acid, methyl methacrylate/ethylacrylate/acrylic acid copolymer, styrene/methyl methacrylate/acrylicacid copolymer, polyvinyl acetate, polyvinylpyrrolidone,polyvinylcaprolactone, polyvinylcaprolactam, derivatives thereof, saltsthereof, and combinations thereof.

In certain embodiments, polymer templates include polystyrenes,including polystyrene and polystyrene copolymers. Polystyrene copolymersinclude copolymers with water-soluble monomers, for examplepolystyrene/acrylic acid, polystyrene/poly(ethylene glycol)methacrylate, and polystyrene/styrene sulfonate.

Present metal oxides include oxides of transition metals, metalloids andrare earths, for example silica, titania, alumina, zirconia, ceria, ironoxides, zinc oxide, indium oxide, tin oxide, chromium oxide, mixed metaloxides, combinations thereof, and the like.

The wt/wt (weight/weight) ratio of polymer nanoparticles to metal oxideis for instance from about 0.1/1 to about 10.0/1 or from about 0.5/1 toabout 10.0/1.

The continuous oil phase comprises for example an organic solvent, asilicone oil or a fluorinated oil. According to the invention “oil”means an organic phase immiscible with water. Organic solvents includehydrocarbons, for example, heptane, hexane, toluene, xylene, and thelike, as well as alkanols such as methanol, ethanol, propanol, etc.

The emulsion droplets are collected, dried and the polymer is removed.Drying is performed for instance via microwave irradiation, in a thermaloven, under vacuum, in the presence of a desiccant or a combinationthereof.

Polymer removal may be performed for example via calcination, pyrolysisor with a solvent (solvent removal). Calcination is performed in someembodiments at temperatures of at least about 200° C., at least about500° C., at least about 1000° C., from about 200° C. to about 1200° C.or from about 200° C. to about 700° C. The calcining can be for asuitable period, e.g., from about 0.1 hour to about 12 hours or fromabout 1 hour to about 8.0 hours. In other embodiments, the calcining canbe for at least about 0.1 hour, at least about 1 hour, at least about 5hours or at least about 10 hours.

Alternatively, a liquid dispersion comprising polymer nanoparticles andmetal oxide is formed with an oil dispersed phase and a continuous waterphase to form an oil-in-water emulsion. The oil droplets may becollected and dried as are aqueous droplets.

Alternatively, a liquid dispersion of polymer nanoparticles and metaloxide is prepared and is spray-dried to form the polymer templatemicrospheres without forming a liquid-in-liquid emulsion. In certainembodiments of spray-drying techniques, a liquid solution or dispersionis fed (e.g. pumped) to an atomizing nozzle associated with a compressedgas inlet. The feed is pumped through the atomizing nozzle to formliquid droplets. The droplets are surrounded by a pre-heated gas in anevaporation chamber, resulting in evaporation of solvent to producesolid particles. The dried particles are carried by the drying gasthrough a cyclone and deposited in a collection chamber. Gases includenitrogen and/or air. In an embodiment of a present spray-drying process,a liquid feed contains a water or oil phase, polymer particles and metaloxide. In an embodiment of a present spray-drying process, a liquid feedcontains a water or oil phase, polymer particles and optionally metaloxide. Provided are polymer template microspheres containing polymernanospheres with metal oxide in the interstitial spaces between thepolymer nanospheres. The polymer nanospheres define the interstitialspaces. Spray-drying techniques include ink jet spray-drying methods andequipment.

In present spray-drying techniques, air may be considered a continuousphase with a dispersed liquid phase (a liquid-in-gas emulsion). Incertain embodiments, spray-drying comprises an inlet temperature of fromany of about 100° C., about 105° C., about 110° C., about 115° C., about120° C., about 130° C., about 140° C., about 150° C., about 160° C. orabout 170° C. to any of about 180° C., about 190° C., about 200° C.,about 210° C., about 215° C. or about 220° C. In some embodiments a pumprate (feed flow rate) of from any of about 1 mL/min, about 2 mL/min,about 5 mL/min, about 6 mL/min, about 8 mL/min, about 10 mL/min, about12 mL/min, about 14 mL/min or about 16 mL/min to any of about 18 mL/min,about 20 mL/min, about 22 mL/min, about 24 mL/min, about 26 mL/min,about 28 mL/min or about 30 mL/min is employed. Spray-drying techniquesare disclosed for example in US2016/0170091.

FIG. 4 is a representation of a spray-drying process according to someembodiments of the invention.

The microspheres are spherical or spherical-like and are micron-scaled,for example having average diameters from about 0.5 microns (μm) toabout 100 μm. The polymer nanoparticles employed as a template are alsospherical, are nano-scaled and are monodisperse, having averagediameters for instance from about 50 nm to about 999 nm. The metal oxideemployed may also be in particle form, which particles may benano-scaled.

The metal oxide of the dispersion may be provided as metal oxide or maybe provided from a metal oxide precursor, for instance via a sol-geltechnique.

Drying of the polymer/metal oxide droplets followed by removal of thepolymer provides microspheres having uniform voids (pores). In general,in the present processes, each droplet provides a single microsphere.The pore diameters are dependent on the size of the polymer particles.Some “shrinkage” or compaction may occur upon polymer removal, providingpore sizes somewhat smaller than the original polymer particle size, forexample from about 10% to about 40% smaller than the polymer particlesize. The pore diameters are uniform as are the polymer particle shapeand size.

Pore diameters may range in some embodiments from about 50 nm to about999 nm.

The average porosity of the present metal oxide microspheres may berelatively high, for example from about 0.10 or about 0.30 to about 0.80or about 0.90. Average porosity of a microsphere means the total porevolume, as a fraction of the volume of the entire microsphere. Averageporosity may be called “volume fraction.”

In some embodiments, a porous microsphere may have a solid core (center)where the porosity is in general towards the exterior surface of themicrosphere. In other embodiments, a porous microsphere may have ahollow core where a major portion of the porosity is towards theinterior of the microsphere. In other embodiments, the porosity may bedistributed throughout the volume of the microsphere. In otherembodiments, the porosity may exist as a gradient, with higher porositytowards the exterior surface of the microsphere and lower or no porosity(solid) towards the center; or with lower porosity towards the exteriorsurface and with higher or complete porosity (hollow) towards thecenter.

For any porous microsphere, the average microsphere diameter is largerthan the average pore diameter, for example, the average microspherediameter is at least about 25 times, at least about 30 times, at leastabout 35 times, or at least about 40 times larger than the average porediameter.

In some embodiments, the ratio of average microsphere diameter toaverage pore diameter is for instance from any of about 40/1, about50/1, about 60/1, about 70/1, about 80/1, about 90/1, about 100/1, about110/1, about 120/1, about 130/1, about 140/1, about 150/1, about 160/1,about 170/1, about 180/1 or about 190/1 to any of about 200/1, about210/1, about 220/1, about 230/1, about 240/1, about 250/1, about 260/1,about 270/1, about 280/1, about 290/1, about 300/1, about 310/1, about320/1, about 330/1, about 340/1 or about 350/1.

Polymer template microspheres comprising monodisperse polymernanospheres may provide, when the polymer is removed, metal oxidemicrospheres having pores that in general have similar pore diameters.

Without wishing to be bound by theory, it is believed that bulk samplesof microspheres exhibit saturated color with reduced unwanted lightscattering when porosity and/or microsphere diameter and/or porediameter are within a certain range. Color properties of a bulk sampleare important, as colorants are employed in bulk, for instance in apaint, an ink, a coating, a cosmetic or a material for a medicalapplication or a security application. In some embodiments, whitemicrospheres are desirable, for example for use as white colorants.

The porous microspheres comprise mainly metal oxide, that is, they mayconsist essentially of or consist of metal oxide. Advantageously, a bulksample of the porous microspheres exhibits color observable by the humaneye. A light absorber may also be present in the microspheres, which mayprovide a more saturated observable color. Absorbers include inorganicand organic pigments, for example a broadband absorber such as carbonblack. Absorbers may for instance be added by physically mixing themicrospheres and the absorbers together or by including the absorbers inthe droplets to be dried. For carbon black, controlled calcination maybe employed to produce carbon black in situ from polymer decomposition.A present microsphere may exhibit no observable color without addedlight absorber and exhibit observable color with added light absorber.

The porous microspheres may be employed as colorants for example foraqueous formulations, oil-based formulations, inks, coatingsformulations, foods, plastics, cosmetics formulations or materials formedical applications or security applications. Coatings formulationsinclude for instance architectural coatings, automotive coatings,varnishes, etc.

The present porous metal oxide microspheres may exhibit angle-dependentcolor or angle-independent color. “Angle-dependent” color means thatobserved color has dependence on the angle of incident light on a sampleor on the angle between the observer and the sample. “Angle-independent”color means that observed color has substantially no dependence on theangle of incident light on a sample or on the angle between the observerand the sample.

Angle-dependent color may be achieved for example with the use ofmonodisperse polymer nanospheres. Angle-dependent color may also beachieved when a step of drying the liquid droplets to provide polymertemplate microspheres is performed slowly, allowing the polymernanospheres to become ordered. Angle-independent color may be achievedwhen a step of drying the liquid droplets is performed quickly, notallowing the polymer nanospheres to become ordered.

For instance, the porous microspheres may comprise from about 60.0 wt %(weight percent) to about 99.9 wt % metal oxide and from about 0.1 wt %to about 40.0 wt % of one or more light absorbers, based on the totalweight of the microspheres.

Advantageously, the porous microspheres may also be monodisperse.

According to the invention, particle size is synonymous with particlediameter and is determined for instance by scanning electron microscopy(SEM) or transmission electron microscopy (TEM). Average particle sizeis synonymous with D50, meaning half of the population resides abovethis point, and half below. Particle size refers to primary particles.Particle size may be measured by laser light scattering techniques, withdispersions or dry powders.

Mercury porosimetry analysis was used to characterize the porosity ofthe microspheres. Mercury porosimetry applies controlled pressure to asample immersed in mercury. External pressure is applied for the mercuryto penetrate into the voids/pores of the material. The amount ofpressure required to intrude into the voids/pores is inverselyproportional to the size of the voids/pores. The mercury porosimetergenerates volume and pore size distributions from the pressure versusintrusion data generated by the instrument using the Washburn equation.For example, porous silica microspheres containing voids/pores with anaverage size of 165 nm have an average porosity of 0.8.

The term “bulk sample” means a population of microspheres. For example,a bulk sample of microspheres is simply a bulk population ofmicrospheres, for instance ≥0.1 mg, ≥0.2 mg, ≥0.3 mg, ≥0.4 mg, ≥0.5 mg,≥0.7 mg, ≥1.0 mg, ≥2.5 mg, ≥5.0 mg, ≥10.0 mg or ≥25.0 mg. A bulk sampleof microspheres may be substantially free of other components. The term“porous microspheres” may mean a bulk sample.

The phrase “exhibits color observable by the human eye” means color willbe observed by an average person. This may be for any bulk sampledistributed over any surface area, for instance a bulk sampledistributed over a surface area of from any of about 1 cm², about 2 cm²,about 3 cm², about 4 cm², about 5 cm² or about 6 cm² to any of about 7cm², about 8 cm², about 9 cm², about 10 cm², about 11 cm², about 12 cm²,about 13 cm², about 14 cm² or about 15 cm². It may also mean observableby a CIE 1931 2° standard observer and/or by a CIE 1964 10° standardobserver. The background for color observation may be any background,for instance a white background, black background or a dark backgroundanywhere between white and black.

The term “of” may mean “comprising”, for instance “a liquid dispersionof” may be interpreted as “a liquid dispersion comprising”.

The terms “microspheres”, “nanospheres”, “droplets”, etc., referred toherein may mean for example a plurality thereof, a collection thereof, apopulation thereof, a sample thereof or a bulk sample thereof.

The term “micro” or “micro-scaled” means from about 0.5 μm to about 999μm. The term “nano” or “nano-scaled” means from about 1 nm to about 999nm.

The terms “spheres” and “particles” may be interchangeable.

The term “monodisperse” in reference to a population of microspheres ornanospheres means particles having generally uniform shapes andgenerally uniform diameters. A present monodisperse population ofmicrospheres or nanospheres for instance may have 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98% or 99% of the particles by number havingdiameters within ±7%, ±6%, ±5%, ±4%, ±3%, ±2% or ±1% of the averagediameter of the population.

A “substrate” may mean an aqueous-based or an oil-based substrate or“media”, which substrate may be a minor part or a major part of a finalcomposition. A substrate may also mean a solid, a semi-solid, a gel, aliquid, a paste, a cream, etc.

Removal of a monodisperse population of polymer nanospheres providesporous metal oxide microspheres having a corresponding population ofpores having an average pore diameter.

The term “substantially free of other components” means for examplecontaining ≤5%, ≤4%, ≤3%, ≤2%, ≤1% or ≤0.5% by weight of othercomponents.

The articles “a” and “an” herein refer to one or to more than one (e.g.at least one) of the grammatical object. Any ranges cited herein areinclusive. The term “about” used throughout is used to describe andaccount for small fluctuations. For instance, “about” may mean thenumeric value may be modified by ±5%, ±4%, ±3%, ±□2%, ±□1%, ±□0.5%,±□0.4%, ±□0.3%, ±□0.2%, ±□0.1% or ±□0.05%. All numeric values aremodified by the term “about” whether or not explicitly indicated.Numeric values modified by the term “about” include the specificidentified value. For example “about 5.0” includes 5.0.

U.S. patents, U.S. patent applications and published U.S. patentapplicants discussed herein are hereby incorporated by reference.

Unless otherwise indicated, all parts and percentages are by weight.Weight percent (wt %), if not otherwise indicated, is based on an entirecomposition free of any volatiles, that is, based on dry solids content.

A non-limiting first set of embodiments of the invention directedtowards methods of preparing porous metal oxide microspheres includes:

In a first embodiment, disclosed is a method to prepare porous metaloxide microspheres comprising a metal oxide, the method comprisingforming a liquid dispersion of polymer nanoparticles and a metal oxide;forming liquid droplets of the dispersion; drying the liquid droplets toprovide polymer template microspheres comprising polymer nanospheres andmetal oxide; and removing the polymer nanospheres from the templatemicrospheres to provide the porous metal oxide microspheres.

In a second embodiment, a method according to the first embodiment,comprising forming a liquid dispersion of polymer nanoparticles and themetal oxide, spray-drying the liquid dispersion to provide polymertemplate microspheres and removing the polymer nanospheres from thetemplate microspheres.

In a third embodiment, a method according to the first embodiment,comprising forming the liquid droplets with a vibrating nozzle. In afourth embodiment, a method according to embodiments 1 to 3, wherein theliquid droplets are aqueous droplets. In a fifth embodiment, a methodaccording to embodiments 1 to 3, wherein the liquid droplets are oildroplets.

In a sixth embodiment, a method according to embodiment 1, comprisingproviding a continuous phase and mixing the liquid dispersion with thecontinuous phase to form an emulsion containing dispersed liquiddispersion droplets. In a seventh embodiment, a method according toembodiment 6, comprising providing a continuous oil phase and mixing anaqueous dispersion with the continuous oil phase to form a water-in-oilemulsion containing aqueous droplets. In an eighth embodiment, a methodaccording to embodiment 6, comprising providing a continuous aqueousphase and mixing an oil dispersion with the continuous phase to form anoil-in-water emulsion containing oil droplets.

In a ninth embodiment, a method according to embodiments 6 to 8,comprising collecting the droplets. In a tenth embodiment, a methodaccording to embodiment 9, comprising drying the droplets to providepolymer template microspheres comprising polymer nanospheres and metaloxide and removing the polymer nanospheres from the templatemicrospheres.

In an eleventh embodiment, a method according to embodiments 6 to 10wherein drying the droplets comprises microwave irradiation, ovendrying, drying under vacuum, drying in the presence of a desiccant, or acombination thereof.

In a twelfth embodiment, a method according to embodiments 7 to 11,wherein the oil phase or dispersion comprises a hydrocarbon, a siliconeoil or a fluorinated oil. In a thirteenth embodiment, a method accordingto embodiments 6 to 12, wherein forming the droplets occurs in amicrofluidic device. In a fourteenth embodiment, a method according toembodiments 6 to 13, wherein forming the droplets occurs in amicrofluidic device which contains a droplet junction having a channelwidth of from any of about 10 μm, about 15 μm, about 20 μm, about 25 μm,about 30 μm, about 35 μm, about 40 μm or about 45 μm to any of about 50μm, about 55 μm, about 60 μm, about 65 μm, about 70 μm, about 75 μm,about 80 μm, about 85 μm, about 90 μm, about 95 μm or about 100 μm. In afifteenth embodiment, a method according to embodiments 13 or 14,comprising collecting the droplets from the microfluidic device.

In a sixteenth embodiment, a method according to any of the precedingembodiments, wherein the wt/wt ratio of polymer nanoparticles to themetal oxide is from any of about 0.1/1, about 0.5/1, about 1.0/1, about1.5/1, about 2.0/1, about 2.5/1 or about 3.0/1 to any of about 3.5/1,about 4.0/1, about 5.0/1, about 5.5/1, about 6.0/1, about 6.5/1, about7.0/1, about 8.0/1, about 9.0/1 or about 10.0/1.

In a seventeenth embodiment, a method according to any of the precedingembodiments, wherein the polymer nanoparticles have an average diameterof from any of about 50 nm, about 75 nm, about 100 nm, about 130 nm,about 160 nm, about 190 nm, about 210 nm, about 240 nm, about 270 nm,about 300 nm, about 330 nm, about 360 nm, about 390 nm, about 410 nm,about 440 nm, about 470 nm, about 500 nm, about 530 nm, about 560 nm,about 590 nm or about 620 nm to any of about 650 nm, about 680 nm, about710 nm, about 740 nm, about 770 nm, about 800 nm, about 830 nm, about860 nm, about 890 nm, about 910 nm, about 940 nm, about 970 nm or about990 nm.

In an eighteenth embodiment, a method according to any of the precedingembodiments, wherein the polymer is selected from the group consistingof poly(meth)acrylic acid, poly(meth)acrylates, polystyrenes,polyacrylamides, polyethylene, polypropylene, polylactic acid,polyacrylonitrile, derivatives thereof, salts thereof, copolymersthereof and combinations thereof.

In a nineteenth embodiment, a method according to any of the precedingembodiments, wherein the polymer is selected from the group consistingof polystyrenes, for example polystyrene copolymers such aspolystyrene/acrylic acid, polystyrene/poly(ethylene glycol) methacrylateor polystyrene/styrene sulfonate. In a twentieth embodiment, a methodaccording to any of the preceding embodiments, wherein the metal oxideis one or more of silica, titania, alumina, zirconia, ceria, ironoxides, zinc oxide, indium oxide, tin oxide or chromium oxide.

In a twenty-first embodiment, a method according to any of the precedingembodiments, wherein the porous microspheres have an average diameter offrom about 0.5 μm to about 100 μm, an average porosity of from about0.10 to about 0.90 or from about 0.10 to about 0.80, and an average porediameter of from about 50 nm to about 999 nm.

In a twenty-second embodiment, a method according to any of thepreceding embodiments, wherein the porous microspheres have an averagediameter of from about 1 μm to about 75 μm, from about 2 μm to about 70μm, from about 3 μm to about 65 μm, from about 4 μm to about 60 μm, fromabout 5 μm to about 55 μm or from about 5 μm to about 50 μm; for examplefrom any of about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm,about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm or about15 μm to any of about 16 μm, about 17 μm, about 18 μm, about 19 μm,about 20 μm, about 21 μm, about 22 μm, about 23 μm, about 24 μm or about25 μm.

In a twenty-third embodiment, a method according to any of the precedingembodiments, wherein the porous microspheres have an average porosity offrom any of about 0.10, about 0.12, about 0.14, about 0.16, about 0.18,about 0.20, about 0.22, about 0.24, about 0.26, about 0.28, about 0.30,about 0.32, about 0.34, about 0.36, about 0.38, about 0.40, about 0.42,about 0.44, about 0.46, about 0.48 about 0.50, about 0.52, about 0.54,about 0.56, about 0.58 or about 0.60 to any of about 0.62, about 0.64,about 0.66, about 0.68, about 0.70, about 0.72, about 0.74, about 0.76,about 0.78, about 0.80 or about 0.90.

In a twenty-fourth embodiment, a method according to any of thepreceding embodiments, wherein the porous microspheres have an averagepore diameter of from any of about 50 nm, about 60 nm, about 70 nm, 80nm, about 100 nm, about 120 nm, about 140 nm, about 160 nm, about 180nm, about 200 nm, about 220 nm, about 240 nm, about 260 nm, about 280nm, about 300 nm, about 320 nm, about 340 nm, about 360 nm, about 380nm, about 400 nm, about 420 nm or about 440 nm to any of about 460 nm,about 480 nm, about 500 nm, about 520 nm, about 540 nm, about 560 nm,about 580 nm, about 600 nm, about 620 nm, about 640 nm, about 660 nm,about 680 nm, about 700 nm, about 720 nm, about 740 nm, about 760 nm,about 780 nm or about 800 nm.

In a twenty-fifth embodiment, a method according to any of the precedingembodiments, wherein the porous microspheres have an average diameter offrom any of about 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm,about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm,about 7.2 μm or about 7.5 μm to any of about 7.8 μm about 8.1 μm, about8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm or about9.9 μm.

In a twenty-sixth embodiment, a method according to any of the precedingembodiments, wherein the porous microspheres have an average porosity offrom any of about 0.45, about 0.47, about 0.49, about 0.51, about 0.53,about 0.55 or about 0.57 to any of about 0.59, about 0.61, about 0.63 orabout 0.65.

In a twenty-seventh embodiment, a method according to any of thepreceding embodiments, wherein the porous microspheres have an averagepore diameter of from any of about 220 nm, about 225 nm, about 230 nm,about 235 nm, about 240 nm, about 245 nm or about 250 nm to any of about255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about280 nm, about 285 nm, about 290 nm, about 295 nm or about 300 nm.

In a twenty-eighth embodiment, a method according to any of thepreceding embodiments, wherein the porous microspheres have an averagediameter of from any of about 4.5 μm, about 4.8 μm, about 5.1 μm, about5.4 μm, about 5.7 μm, about 6.0 μm, about 6.3 μm, about 6.6 μm, about6.9 μm, about 7.2 μm or about 7.5 μm to any of about 7.8 μm about 8.1μm, about 8.4 μm, about 8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μmor about 9.9 μm; an average porosity of from any of about 0.45, about0.47, about 0.49, about 0.51, about 0.53, about 0.55 or about 0.57 toany of about 0.59, about 0.61, about 0.63 or about 0.65; and an averagepore diameter of from any of about 220 nm, about 225 nm, about 230 nm,about 235 nm, about 240 nm, about 245 nm or about 250 nm to any of about255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm, about280 nm, about 285 nm, about 290 nm, about 295 nm or about 300 nm.

In a twenty-ninth embodiment, a method according to any of the precedingembodiments, wherein the porous microspheres comprise from any of about60.0 wt % to about 99.9 wt % metal oxide, for example comprising fromany of about 60.0 wt %, about 64.0 wt %, about 67.0 wt %, about 70.0 wt%, about 73.0 wt %, about 76.0 wt %, about 79.0 wt %, about 82.0 wt % orabout 85.0 wt % to any of about 88.0 wt %, about 91.0 wt %, about 94.0wt %, about 97.0 wt %, about 98.0 wt %, about 99.0 wt % or about 99.9 wt% metal oxide, based on the total weight of the microspheres.

In a thirtieth embodiment, a method according to any of the precedingembodiments, wherein the porous microspheres comprise from about 0.1 wt% to about 40.0 wt % of one or more light absorbers, for examplecomprising from any of about 0.1 wt %, about 0.3 wt %, about 0.5 wt %,about 0.7 wt %, about 0.9 wt %, about 1.0 wt %, about 1.5 wt %, about2.0 wt %, about 2.5 wt %, about 5.0 wt %, about 7.5 wt %, about 10.0 wt%, about 13.0 wt %, about 17.0 wt %, about 20.0 wt % or about 22.0 wt %to any of about 24.0 wt %, about 27.0 wt %, about 29.0 wt %, about 31.0wt %, about 33.0 wt %, about 35.0 wt %, about 37.0 wt %, about 39.0 wt %or about 40.0 wt % of one or more light absorbers, based on the totalweight of the microspheres.

In a thirty-first embodiment, a method according to any of the precedingembodiments, wherein the porous microspheres comprise one or more lightabsorbers selected from the group consisting of inorganic and organicpigments, for example carbon black.

In a thirty-second embodiment, a method according to any of thepreceding embodiments, wherein a bulk sample of the porous microspheresexhibits color observable by the human eye. In a thirty-thirdembodiment, a method according to any of the preceding embodiments,wherein a bulk sample of the porous microspheres exhibitsangle-independent color observable by the human eye. In a thirty-fourthembodiment, a method according to any of embodiments 1-32, wherein abulk sample of the porous microspheres exhibits angle-dependent colorobservable by the human eye.

In a thirty-fifth embodiment, a method according to any of the precedingembodiments, wherein the porous microspheres are monodisperse. In athirty-sixth embodiment, a method according to any of the precedingembodiments, wherein the porous metal oxide microspheres are a bulksample of microspheres.

In a thirty-seventh embodiment, a method according to any of thepreceding embodiments, wherein removing the polymer nanospheres from thetemplate microspheres comprises calcination, pyrolysis or solventremoval.

In a thirty-eighth embodiment, a method according to any of thepreceding embodiments, wherein removing the polymer nanospherescomprises calcining the template microspheres at temperatures of fromany of about 200° C., about 350° C., about 400° C., 450° C., about 500°C. or about 550° C. to any of about 600° C., about 650° C., about 700°C. or about 1200° C. for a period of from any of about 0.1 h (hour), 1h, about 1.5 h, about 2.0 h, about 2.5 h, about 3.0 h, about 3.5 h orabout 4.0 h to any of about 4.5 h, about 5.0 h, about 5.5 h, about 6.0h, about 6.5 h, about 7.0 h, about 7.5 h about 8.0 h or about 12 h.Alternatively, the calcining can be at temperatures of at least about200° C., at least about 500° C., or at least about 1000° C., for asuitable period, e.g., for at least about 0.1 hour, at least about 1hour, at least about 5 hours or at least about 10 hours.

In a thirty-ninth embodiment, disclosed are porous microspheres preparedaccording to any of the preceding methods. In a fortieth embodiment,disclosed is a bulk sample of porous microspheres prepared according toany of the preceding methods.

A non-limiting second set of embodiments of the invention directedtowards porous metal oxide microspheres includes:

In a first embodiment, porous microspheres comprising a metal oxide,wherein the microspheres have an average diameter of from about 0.5 μmto about 100 μm, an average porosity of from about 0.10 to about 0.90 orfrom about 0.10 to about 0.80 and an average pore diameter of from about50 nm to about 999 nm.

In a second embodiment, disclosed are porous microspheres according toembodiment 1, which have an average diameter of from about 1 μm to about75 μm, about 2 μm to about 70 μm, from about 3 μm to about 65 μm, fromabout 4 μm to about 60 μm, from about 5 μm to about 55 μm or from about5 μm to about 50 μm; for example from any of about 5 μm, about 6 μm,about 7 μm, about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12μm, about 13 μm, about 14 μm or about 15 μm to any of about 16 μm, about17 μm, about 18 μm, about 19 μm, about 20 μm, about 21 μm, about 22 μm,about 23 μm, about 24 μm or about 25 μm.

In a third embodiment, the porous microspheres according to embodiments1 or 2, which have an average porosity of from any of about 0.10, about0.12, about 0.14, about 0.16, about 0.18, about 0.20, about 0.22, about0.24, about 0.26, about 0.28, about 0.30, about 0.32, about 0.34, about0.36, about 0.38, about 0.40, about 0.42, about 0.44, about 0.46, about0.48 about 0.50, about 0.52, about 0.54, about 0.56, about 0.58 or about0.60 to any of about 0.62, about 0.64, about 0.66, about 0.68, about0.70, about 0.72, about 0.74, about 0.76, about 0.78, about 0.80 orabout 0.90.

In a fourth embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average pore diameter of from anyof about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 100 nm,about 120 nm, about 140 nm, about 160 nm, about 180 nm, about 200 nm,about 220 nm, about 240 nm, about 260 nm, about 280 nm, about 300 nm,about 320 nm, about 340 nm, about 360 nm, about 380 nm, about 400 nm,about 420 nm or about 440 nm to any of about 460 nm, about 480 nm, about500 nm, about 520 nm, about 540 nm, about 560 nm, about 580 nm, about600 nm, about 620 nm, about 640 nm, about 660 nm, about 680 nm, about700 nm, about 720 nm, about 740 nm, about 760 nm, about 780 nm or about800 nm.

In a fifth embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average diameter of from any ofabout 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm,about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm orabout 7.5 μm to any of about 7.8 μm about 8.1 μm, about 8.4 μm, about8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm or about 9.9 μm. In asixth embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average porosity of from any ofabout 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55or about 0.57 to any of about 0.59, about 0.61, about 0.63 or about0.65. In a seventh embodiment, the porous microspheres according to anyof the preceding embodiments, which have an average pore diameter offrom any of about 220 nm, about 225 nm, about 230 nm, about 235 nm,about 240 nm, about 245 nm or about 250 nm to any of about 255 nm, about260 nm, about 265 nm, about 270 nm, about 275 nm, about 280 nm, about285 nm, about 290 nm, about 295 nm or about 300 nm.

In an eighth embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average diameter of from any ofabout 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm,about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm orabout 7.5 μm to any of about 7.8 μm about 8.1 μm, about 8.4 μm, about8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm or about 9.9 μm; andwhich have an average porosity of from any of about 0.45, about 0.47,about 0.49, about 0.51, about 0.53, about 0.55 or about 0.57 to any ofabout 0.59, about 0.61, about 0.63 or about 0.65; and which have anaverage pore diameter of from any of about 220 nm, about 225 nm, about230 nm, about 235 nm, about 240 nm, about 245 nm or about 250 nm to anyof about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm,about 280 nm, about 285 nm, about 290 nm, about 295 nm or about 300 nm.

In a ninth embodiment, the porous microspheres according to any of thepreceding embodiments, comprising from about 60.0 wt % to about 99.9 wt% metal oxide, for example comprising from any of about 60.0 wt %, about64.0 wt %, about 67.0 wt %, about 70.0 wt %, about 73.0 wt %, about 76.0wt %, about 79.0 wt %, about 82.0 wt % or about 85.0 wt % to any ofabout 88.0 wt %, about 91.0 wt %, about 94.0 wt %, about 97.0 wt %,about 98.0 wt %, about 99.0 wt % or about 99.9 wt % metal oxide, basedon the total weight of the microspheres.

In a tenth embodiment, the porous microspheres according to any of thepreceding embodiments, wherein the metal oxide is selected from thegroup consisting of silica, titania, alumina, zirconia, ceria, ironoxides, zinc oxide, indium oxide, tin oxide, chromium oxide andcombinations thereof. In an eleventh embodiment, the porous microspheresaccording to any of the preceding embodiments, wherein the metal oxideis selected from the group consisting of silica, titania, alumina andcombinations thereof.

In a twelfth embodiment, the porous microspheres according to any of thepreceding embodiments, comprising from about 0.1 wt % to about 40.0 wt %of one or more light absorbers, for example comprising from any of about0.1 wt %, about 0.3 wt %, about 0.5 wt %, about 0.7 wt %, about 0.9 wt%, about 1.0 wt %, about 1.5 wt %, about 2.0 wt %, about 2.5 wt %, about5.0 wt %, about 7.5 wt %, about 10.0 wt %, about 13.0 wt %, about 17.0wt %, about 20.0 wt % or about 22.0 wt % to any of about 24.0 wt %,about 27.0 wt %, about 29.0 wt %, about 31.0 wt %, about 33.0 wt %,about 35.0 wt %, about 37.0 wt %, about 39.0 wt % or about 40.0 wt % ofone or more light absorbers, based on the total weight of themicrospheres. In a thirteenth embodiment, the porous microspheresaccording to any of the preceding embodiments, comprising one or morelight absorbers selected from the group consisting of inorganic andorganic pigments, for example carbon black.

In a fourteenth embodiment, the porous microspheres according to any ofthe preceding embodiments, wherein a bulk sample of the porousmicrospheres exhibits color observable by the human eye. In a fifteenthembodiment, the porous microspheres according to any of the precedingembodiments, wherein a bulk sample of the porous microspheres exhibitsangle-independent color observable by the human eye. In a sixteenthembodiment, the porous microspheres according to any of embodiments1-14, wherein a bulk sample of the porous microspheres exhibitsangle-dependent color observable by the human eye.

In a seventeenth embodiment, the porous microspheres according to any ofthe preceding embodiments which are monodisperse. In an eighteenthembodiment, a composition comprising a substrate and the porousmicrospheres according to any of the preceding embodiments. In anineteenth embodiment, a composition according to embodiment 18, whichis an aqueous formulation, an oil-based formulation, an ink, a coatingformulation, a food, a plastic, a cosmetic formulation or a material fora medical application or a security application.

A non-limiting third set of embodiments of the disclosure directedtowards porous metal oxide microspheres includes:

In a first embodiment, disclosed are porous microspheres comprising ametal oxide, wherein a bulk sample of the porous microspheres exhibitscolor observable by the human eye.

In a second embodiment, the porous microspheres according to embodiment1, wherein the microspheres have an average diameter of from about 0.5μm to about 100 μm, an average porosity of from about 0.10 to about 0.90or from about 0.10 to about 0.80 and an average pore diameter of fromabout 50 nm to about 999 nm.

In a third embodiment, the porous microspheres according to embodiments1 or 2, which have an average diameter of from about 1 μm to about 75μm, about 2 μm to about 70 μm, from about 3 μm to about 65 μm, fromabout 4 μm to about 60 μm, from about 5 μm to about 55 μm or from about5 μm to about 50 μm; for example from any of about 5 μm, about 6 μm,about 7 μm, about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12μm, about 13 μm, about 14 μm or about 15 μm to any of about 16 μm, about17 μm, about 18 μm, about 19 μm, about 20 μm, about 21 μm, about 22 μm,about 23 μm, about 24 μm or about 25 μm.

In a fourth embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average porosity of from any ofabout 0.10, about 0.12, about 0.14, about 0.16, about 0.18, about 0.20,about 0.22, about 0.24, about 0.26, about 0.28, about 0.30, about 0.32,about 0.34, about 0.36, about 0.38, about 0.40, about 0.42, about 0.44,about 0.46, about 0.48 about 0.50, about 0.52, about 0.54, about 0.56,about 0.58 or about 0.60 to any of about 0.62, about 0.64, about 0.66,about 0.68, about 0.70, about 0.72, about 0.74, about 0.76, about 0.78,or about 0.80 or about 0.90.

In a fifth embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average pore diameter of from anyof about 50 nm, about 60 nm, about 70 nm, about 80 nm, about 100 nm,about 120 nm, about 140 nm, about 160 nm, about 180 nm, about 200 nm,about 220 nm, about 240 nm, about 260 nm, about 280 nm, about 300 nm,about 320 nm, about 340 nm, about 360 nm, about 380 nm, about 400 nm,about 420 nm or about 440 nm to any of about 460 nm, about 480 nm, about500 nm, about 520 nm, about 540 nm, about 560 nm, about 580 nm, about600 nm, about 620 nm, about 640 nm, about 660 nm, about 680 nm, about700 nm, about 720 nm, about 740 nm, about 760 nm, about 780 nm or about800 nm.

In a sixth embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average diameter of from any ofabout 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm,about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm orabout 7.5 μm to any of about 7.8 μm about 8.1 μm, about 8.4 μm, about8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm or about 9.9 μm. In aseventh embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average porosity of from any ofabout 0.45, about 0.47, about 0.49, about 0.51, about 0.53, about 0.55or about 0.57 to any of about 0.59, about 0.61, about 0.63 or about0.65. In an eighth embodiment, the porous microspheres according to anyof the preceding claims, which have an average pore diameter of from anyof about 220 nm, about 225 nm, about 230 nm, about 235 nm, about 240 nm,about 245 nm or about 250 nm to any of about 255 nm, about 260 nm, about265 nm, about 270 nm, about 275 nm, about 280 nm, about 285 nm, about290 nm, about 295 nm or about 300 nm.

In a ninth embodiment, the porous microspheres according to any of thepreceding embodiments, which have an average diameter of from any ofabout 4.5 μm, about 4.8 μm, about 5.1 μm, about 5.4 μm, about 5.7 μm,about 6.0 μm, about 6.3 μm, about 6.6 μm, about 6.9 μm, about 7.2 μm orabout 7.5 μm to any of about 7.8 μm about 8.1 μm, about 8.4 μm, about8.7 μm, about 9.0 μm, about 9.3 μm, about 9.6 μm or about 9.9 μm; andwhich have an average porosity of from any of about 0.45, about 0.47,about 0.49, about 0.51, about 0.53, about 0.55 or about 0.57 to any ofabout 0.59, about 0.61, about 0.63 or about 0.65; and which have anaverage pore diameter of from any of about 220 nm, about 225 nm, about230 nm, about 235 nm, about 240 nm, about 245 nm or about 250 nm to anyof about 255 nm, about 260 nm, about 265 nm, about 270 nm, about 275 nm,about 280 nm, about 285 nm, about 290 nm, about 295 nm or about 300 nm.

In a tenth embodiment, the porous microspheres according to any of thepreceding embodiments, comprising from about 60.0 wt % to about 99.9 wt% metal oxide, for example comprising from any of about 60.0 wt %, about64.0 wt %, about 67.0 wt %, about 70.0 wt %, about 73.0 wt %, about 76.0wt %, about 79.0 wt %, about 82.0 wt % or about 85.0 wt % to any ofabout 88.0 wt %, about 91.0 wt %, about 94.0 wt %, about 97.0 wt %,about 98.0 wt %, about 99.0 wt % or about 99.9 wt % metal oxide, basedon the total weight of the microspheres.

In an eleventh embodiment, the porous microspheres according to any ofthe preceding embodiments, wherein the metal oxide is selected from thegroup consisting of silica, titania, alumina, zirconia, ceria, ironoxides, zinc oxide, indium oxide, tin oxide, chromium oxide andcombinations thereof. In a twelfth embodiment, the porous microspheresaccording to any of the preceding embodiments, wherein the metal oxideis selected from the group consisting of silica, titania, alumina andcombinations thereof.

In a thirteenth embodiment, the porous microspheres according to any ofthe preceding embodiments, comprising from about 0.1 wt % to about 40.0wt % of one or more light absorbers, for example comprising from any ofabout 0.1 wt %, about 0.3 wt %, about 0.5 wt %, about 0.7 wt %, about0.9 wt %, about 1.0 wt %, about 1.5 wt %, about 2.0 wt %, about 2.5 wt%, about 5.0 wt %, about 7.5 wt %, about 10.0 wt %, about 13.0 wt %,about 17.0 wt %, about 20.0 wt % or about 22.0 wt % to any of about 24.0wt %, about 27.0 wt %, about 29.0 wt %, about 31.0 wt %, about 33.0 wt%, about 35.0 wt %, about 37.0 wt %, about 39.0 wt % or about 40.0 wt %of one or more light absorbers, based on the total weight of themicrospheres. In a fourteenth embodiment, the porous microspheresaccording to any of the preceding embodiments, comprising one or morelight absorbers selected from the group consisting of inorganic andorganic pigments, for example carbon black.

In a sixteenth embodiment, the porous microspheres according to any ofthe preceding embodiments, wherein a bulk sample of the porousmicrospheres exhibits color observable by the human eye.

In a seventeenth embodiment, porous microspheres according to any of thepreceding embodiments which are monodisperse.

In an eighteenth embodiment, porous microspheres according to any of thepreceding embodiments, wherein a bulk sample of the porous microspheresexhibits angle-independent color observable by the human eye. In anineteenth embodiment, porous microspheres according to any ofembodiments 1-17, wherein a bulk sample of the porous microspheresexhibits angle-dependent color observable by the human eye.

In a twentieth embodiment, a composition comprising a substrate and theporous microspheres according to any of the preceding embodiments. In atwenty-first embodiment, a composition according to embodiment 20, whichis an aqueous formulation, an oil-based formulation, a coatingformulation, a food, an ink, a plastic, a cosmetic formulation or amaterial for a medical application or a security application.

EXAMPLES Example 1 Porous Silica Microspheres

A styrene/acrylic acid copolymer is prepared as follows: 230 mLdeionized (DI) water is added to a 3-neck reaction flask equipped with athermometer, condenser, magnetic stirring and nitrogen atmosphere. Thewater is heated to 80° C. and 10 g of styrene are added with stirring,followed by 100 mg acrylic acid dissolved in 10 mL DI water via syringe.100 mg of ammonium persulfate is dissolved in 10 mL DI water and addedto the stirred mixture via syringe. The reaction mixture is stirred for24 hours at 80° C. The polymer colloid dispersion is allowed to cool toroom temperature and is purified via centrifugation, producingpolystyrene nanospheres having an average particle size of 250 nm.

The aqueous polystyrene colloid dispersion is diluted to 1 wt % withdeionized water and 1 wt % silica nanoparticles are added and themixture is sonicated to prevent particle agglomeration. A continuous oilphase contains 0.1 wt % polyethylene glycol/perfluoropolyethersurfactant in a fluorinated oil. The aqueous colloid dispersion and oilare each injected into a microfluidic device having a 50 μm dropletjunction via syringes associated with pumps. The system is allowed toequilibrate until monodisperse droplets are produced. The monodispersedroplets are collected in a reservoir.

Collected droplets are dried in an oven at 45° C. for 4 hours to providemonodisperse polymer template microspheres. The polymer templatemicrospheres are calcined by placing on a silicon wafer, heating fromroom temperature to 500° C. over a 3 hour period, holding at 500° C. for2 hours, and cooling back to room temperature over a 3 hour period.Provided are monodisperse silica microspheres having an average diameterof 15 microns.

FIG. 2 and FIG. 3 are scanning electron microscope (SEM) images of apolymer template microsphere and a porous silica microsphere prepared ina similar fashion.

Example 2 Porous Silica Microspheres Containing a Light Absorber

The product of Example 1 is physically mixed with an aqueous dispersionof carbon black or with a carbon black powder at varying weight levels.Provided are monodisperse porous silica microspheres containing carbonblack at levels of 0.5 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt % and 5 wt %,based on the total weight of the microspheres.

Example 3 Drying Methods

Examples 1 and 2 are repeated, wherein the drying step employs microwaveirradiation, drying under vacuum and/or drying in the presence of adesiccant.

Example 4 Preparation of Porous Silica Microspheres Via Spray-Drying

A styrene/acrylic acid copolymer is prepared as follows: 230 mLdeionized (DI) water is added to a 3-neck reaction flask equipped with athermometer, condenser, magnetic stirring and nitrogen atmosphere. Thewater is heated to 80° C. and 10 g of styrene are added with stirring,followed by 100 mg acrylic acid dissolved in 10 mL DI water via syringe.100 mg of ammonium persulfate is dissolved in 10 mL DI water and addedto the stirred mixture via syringe. The reaction mixture is stirred for24 hours at 80° C. The polymer colloid dispersion is allowed to cool toroom temperature and is purified via centrifugation, producingpolystyrene nanospheres having an average particle size of 250 nm.

The aqueous polystyrene colloid dispersion is diluted to 1 wt % withdeionized water and 1 wt % silica nanoparticles are added and themixture is sonicated to prevent particle agglomeration. The aqueousdispersion is spray-dried to provide polymer template microspherescomprising polymer nanospheres and silica. The microspheres are calcinedby heating from room temperature to 500° C. over a 3 hour period,holding at 500° C. for 2 hours, and cooling back to room temperatureover a 3 hour period. Provided are porous silica microspheres.

Example 5 Visible Color in a Bulk Sample

In these bulk color examples, 0.5 milligrams of porous microspheres areevenly placed in a 10 mL clear glass vial having a 6 cm² bottom surface.The color is observed with the human eye.

Two samples of porous silica microspheres are prepared in a similarfashion to Example 1, wherein the wt/wt ratio of polymer to silica is1:1 and 3:1, respectively. The 1:1 wt/wt sample is white and the 3:1wt/wt sample exhibits a distinct blue color.

A sample of porous silica microspheres is prepared according to Example1, where the polystyrene nanospheres have an average particle size of360 nm and the wt/wt ratio of polymer to silica is 3:1. The sampleexhibits a distinct green color.

Porous silica microspheres are prepared in a similar fashion to Example4, where the polystyrene nanospheres have an average particle size of360 nm. With a wt/wt ratio of polymer to silica of 4:1, the porousmicrospheres have a porosity of 0.55 and exhibit a distinct green color.With a wt/wt ratio of polymer to silica is 2:1, the porous microsphereshave a porosity of 0.45 and exhibit a distinct orange color.

Example 6 Zinc Oxide Porous Microspheres

A sample of porous zinc oxide microspheres is prepared according to theprocedure of Example 4, replacing silica with zinc oxide and where thepolystyrene nanospheres have an average particle size of 230 nm and awt/wt ratio of polymer to zinc oxide of 1:2. A 0.5 mg sample of porousmicrospheres are evenly placed in a 10 mL clear glass vial having a 6cm² bottom surface. The sample exhibits a distinct blue color to thehuman eye.

Example 7 Silica/Titania Porous Microspheres

A sample of porous microspheres containing silica and titania isprepared according to the process of Example 1, wherein the wt/wt ratioof polymer to total metal oxide is 3:1. The wt/wt ratio of silica totitania is 9:1.

The invention claimed is:
 1. Porous microspheres comprising a metaloxide, wherein the porous microspheres have: an average diameter of fromabout 1 μm to about 75 μm; an average porosity of from about 0.45 toabout 0.8; and an average pore diameter of from about 50 nm to about 800nm, wherein the porosity of each porous microsphere is distributedthroughout the volume of the porous microsphere.
 2. The porousmicrospheres of claim 1, wherein the porous microspheres have an averagediameter of from about 1 μm to about 50 μm.
 3. The porous microspheresof claim 1, wherein the porous microspheres have an average porediameter of from about 50 nm to about 500 nm.
 4. The porous microspheresof claim 1, wherein the porous microspheres have an average porosity offrom about 0.45 to about 0.65.
 5. The porous microspheres of claim 1,wherein the porous microspheres have: an average diameter of from about4.5 μm to about 9.9 μm; an average porosity of from about 0.45 to about0.65; and an average pore diameter of from about 220 nm to about 300 nm.6. The porous microspheres of claim 1, comprising from about 60.0 wt %to about 99.9 wt % of the metal oxide, based on the total weight of theporous microspheres.
 7. The porous microspheres of claim 1, wherein themetal oxide is selected from the group consisting of silica, titania,alumina, zirconia, ceria, iron oxide, zinc oxide, indium oxide, tinoxide, chromium oxide, and combinations thereof.
 8. The porousmicrospheres of claim 1, wherein the metal oxide is selected from thegroup consisting of silica, titania, alumina, ceria, iron oxide, zincoxide, and combinations thereof.
 9. The porous microspheres of claim 1,wherein the porous microspheres are monodisperse.
 10. A compositioncomprising: a substrate; and porous microspheres comprising a metaloxide, wherein the porous microspheres have: an average diameter of fromabout 1 μm to about 75 μm; an average porosity of from about 0.45 toabout 0.8; and an average pore diameter of from about 50 nm to about 800nm, wherein the porosity of each porous microsphere is distributedthroughout the volume of the porous microsphere.
 11. The composition ofclaim 10, wherein the composition is an aqueous formulation, anoil-based formulation, an ink, a coating formulation, a food, a plastic,a cosmetic formulation, or a material for a medical application or asecurity application.
 12. The composition of claim 10, furthercomprising one or more light absorbers.
 13. The composition of claim 12,wherein the one or more light absorbers are present from about 0.1 wt %to about 40.0 wt %, based on the total weight of the porousmicrospheres.
 14. The composition of claim 10, wherein a bulk sample ofthe composition exhibits angle-dependent color observable by a humaneye.
 15. The composition of claim 10, wherein a bulk sample of thecomposition exhibits angle-independent color observable by a human eye.16. The composition of claim 10, wherein the metal oxide is selectedfrom the group consisting of silica, titania, alumina, ceria, ironoxide, zinc oxide, and combinations thereof.
 17. The composition ofclaim 10, wherein the porous microspheres are monodisperse.
 18. Thecomposition of claim 10, wherein the porous microspheres have an averagediameter of from about 1 μm to about 50 μm.
 19. The composition of claim10, wherein the porous microspheres have an average pore diameter offrom about 50 nm to about 500 nm.
 20. The composition of claim 10,wherein the porous microspheres have an average porosity of from about0.45 to about 0.65.